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	<div id="winchm_template_title">Breaking Into the Debugger</div>
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	<div id="winchm_template_content"><div id="mainSection"><p>User-mode and kernel-mode code use different routines to break into the debugger.</p>
<h3><a id="user_mode_break_routines"></a><a id="USER_MODE_BREAK_ROUTINES"></a>User-Mode Break Routines</h3>
<p>A break routine causes an exception to occur in the current process, so that the calling thread can signal the debugger associated with the calling process.</p>
<p>To break into a debugger from a user-mode program, use the <b>DebugBreak</b> routine. For complete documentation of this routine, see the Microsoft Windows SDK.</p>
<p>When a user-mode program calls <b>DebugBreak</b>, the following possible actions will occur:</p>
<ol>
<li>
<p>If a user-mode debugger is attached, the program will break into the debugger. This means that the program will pause and the debugger will become active.</p>
</li>
<li>
<p>If no user-mode debugger is attached, but kernel-mode debugging was enabled at boot time, the entire computer will break into the kernel debugger. If no kernel debugger is attached, the computer will freeze and await a kernel debugger.</p>
</li>
<li>
<p>If no user-mode debugger is attached, and kernel-mode debugging is not enabled, the program will terminate with an unhandled exception, and the post-mortem (just-in-time) debugger will be activated. For more information, see <a href="#Bookmark1263">Enabling Postmortem Debugging</a>.</p>
</li>
</ol>
<h3><a id="kernel_mode_break_routines"></a><a id="KERNEL_MODE_BREAK_ROUTINES"></a>Kernel-Mode Break Routines</h3>
<p>When a kernel-mode program breaks into the debugger, the entire operating system freezes until the kernel debugger allows execution to resume. If no kernel debugger is present, this is treated as a bug check.</p>
<p>The <b>DbgBreakPoint</b> routine works in kernel-mode code, but is otherwise similar to the <b>DebugBreak</b> user-mode routine.</p>
<p><b>DbgBreakPointWithStatus</b> also causes a break, but it additionally sends a 32-bit status code to the debugger.</p>
<p><b>KdBreakPoint</b> and <b>KdBreakPointWithStatus</b> are identical to <b>DbgBreakPoint</b> and <b>DbgBreakPointWithStatus</b>, respectively, when compiled in the checked build environment. When compiled in the free build environment, they have no effect.</p>
<p>For complete documentation of these routines, as well as the build environment, see the Windows Driver Kit.</p>
<h3><a id="kernel_mode_conditional_break_routines"></a><a id="KERNEL_MODE_CONDITIONAL_BREAK_ROUTINES"></a>Kernel-Mode Conditional Break Routines</h3>
<p>Two conditional break routines are available for kernel-mode code. These routines test a logical expression. If the expression is false, execution halts and the debugger becomes active.</p>
<p>The <b>ASSERT</b> macro causes the debugger to display the failed expression and its location in the program. The <b>ASSERTMSG</b> macro is similar, but allows an additional message to be sent to the debugger.</p>
<p><b>ASSERT</b> and <b>ASSERTMSG</b> are only active when compiled in the checked build environment. When compiled in the free build environment, they have no effect.</p>
<p>For complete documentation of these routines, as well as the build environment, see the Windows Driver Kit.</p></div></div>	
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